1. Field of the Invention
The present invention relates to a display control system for setting a gray scale level, which system is especially suitable for use in a portable computer.
2. Description of the Related Art
In the field of portable computers, so-called lap-top type computers which are compact, lightweight, and convenient for carrying, have become popular in place of conventional desk-top type computers. As a display device for this portable computer, a flat panel display such as a liquid crystal display (LCD) or a plasma display is used. Therefore, a multi-gradation display is made upon designation of most of application programs which are capable of multi-color display.
Conventionally, gray scale levels are set and changed using a special-purpose tool. After a system is started, a program for installing the special-purpose tool is executed on the operating system, so that the tool (gray scale level setting/changing program; to be simply referred to as VCHAD hereinafter) is resident in a main memory. Thereafter, a user executes specific key operations as needed to start the VCHAD program. The VCHAD program presents all the currently used display set values one by one, thus urging the user to perform a setting operation. Values set by the user are reflected on an actual screen display in a real-time manner.
In addition to the VCHAD, an environmental setting program (setup program) inherent to a system may be adopted. With the setup program, individual set values cannot be set. The setup program has some combinations of set values, which are generally determined to be proper, as inherent values, and a user selects one of these inherent values. The selection made by the user is stored in a back-up memory, and thereafter, the system is rebooted to set various display set values. Therefore, an actual screen display according to the user's selection is obtained after setup processing and reboot processing.
In the above-mentioned prior arts, in the former method, the VCHAD program must be resident in the memory. For example, when a display method is changed during execution of another application software program, if the VCHAD program is not resident in the memory, a user must give up this change, or temporarily ends the currently executed application software program, and must execute the VCHAD installation program. Thereafter, the user must change the display method. The VCHAD program requests setting of all the display set values which are currently used. More specifically, in a gray scale display capable of displaying 16 levels, a maximum of 16 set values are necessary. It is very difficult and cumbersome for a user who is not accustomed with a computer to designate a proper display method while balancing all these set values.
In the latter method, i.e., when the setup program is used, the content selected by a user does not appear in real time on an actual display screen. Therefore, the user cannot immediately determine optimal selection. Since the system must be rebooted, if the user performs some unique setting operations, all these set values are undesirably lost. For example, when the user sets a baud rate or the number of bits of start or stop bits in an application program for performing a communication, if gray scale levels are changed in the setup processing, various parameters set by the user are reset to default values after the reboot operation.